Ceramic electrical resistor roll for copying machine

ABSTRACT

An electrostatic copying assembly including a pair of adjacent, parallel and oppositely driven rolls, one of which has a radially outer portion of fired silicate clay base ceramic material which is doped with iron oxide and a radially inner portion of conductive material to form part of the charging circuit.

United States Patent 1 3,697,836

Moss et al. 145) Oct. 10, 1972 [54] CERAMIC ELECTRICAL RESISTOR [56] References Cited ROLL FOR COPYING MACHINE UNITED STATES PATENTS [72] Inventors: James R. Moss; Richard F. Roe;

Lawrence Cuubmugh, n of 2,590,894 4/1952 Sanbom [06/46 X Robe" w Buck wheatridge 3,521,]26 7/1970 Granzoe et al ..3l7/262 A all of Colo. Primary ExaminerL. T. Hix [73] Assignee: goillrs Porcelain C p y, Golden, AtmrneyMcGlynn, Reising, Milton & Ethington [22] Filed: June 3, 1970 ABSTRACT [21] APPL 43,083 An electrostatic copying assembly including a pair of adjacent, parallel and oppositely driven rolls. one of which has a radially outer portion of fired silicate clay [52] US. Cl ..3l7/262 A, 106/46, 252/519 base ceramiC material Which is doped with iron Oxide [5 15/02 Hmb C04) 33/26 and a radially inner portion of conductive material to [58] Field of Search ..3l7/262 A, 3, 4, 262 R;

DEVELOPER form part of the charging circuit.

6 Claims, 2 Drawing Figures SUPPLY PATENTED I972 3.697.836

DEVELOPER POWER SUPPLY lNVENTORS (ll mes K. Jfoss,

TTORNEYS CERAMIC ELECTRICAL RESISTOR ROLL FOR COPYING MACHINE This invention relates to electrostatic copying of printed matter and the like and particularly to the construction of a roll by which the electrostatic charge is applied.

lt is well known that printed matter and the like may be copied employing a process which involves the formation or application of an electrostatic charge across a specially prepared copying paper, the exposure of the copying paper to the material to be copied, the subsequent exposure of the paper to a light source and the development of the exposed paper to produce the visible image. it is common in such apparatus to apply the electrostatic charge to the copying paper by means of a corona discharge. The apparatus involved in creating the corona discharge is, however, subject to chemical corrosion and fouling by dust and thus may require inordinate maintenance. Another manner of applying the electrostatic charge involves the use of a semi-conductive roll which physically contacts the paper. Such rolls have been fabricated from various elastomeric materials and metals. However, where elastomeric materials are used it has been found that the surface discharge tends to harden and crack the surface of the rolls and alter the electrical properties thereof. in the case of metals such as stainless steel, again the surface tends to etch rather rapidly and optical resolution deteriorates along with this etching.

In accordance with the present invention, a roll for the direct contact application of electrostatic charge to a copying paper is provided having the proper electrical qualities along with the proper and long-lived physical surface characteristics. in general, the invention involves the fabrication of an electrostatic copying roll for use in preparing copies of printed material and the like in which the roll comprises a radially outer portion of fired silicate clay base ceramic material which is doped with a metal oxide and a radially inner portion of conductive material for connection to a charging circuit.

It is preferred that the subject roll be fabricated by compacting air dried clay base ceramic powder mixed with iron oxide and firing the compacted roll according to a predetermined schedule, later metalizing the interior diameter of the roll to accept a conductive element therein, and surface treating as necessary the outer diameter of the roll to produce the desired physical characteristics thereof.

The various features and advantages of the invention will be best understood by reference to the following specification which describes the properties, characteristics and fabrication method of a preferred embodiment of the subject invention and is to be taken with the accompanying drawings of which:

FIG. 1 is a schematic diagram of a copying assembly employing the subject roll; and

FIG. 2 is a sectional view of the roll apparatus of FIG. I looking a section line 2-2.

Referring to the figures, electrostatic copying assembly is shown to comprise a chassis 12 supporting elongate cylindrical rolls l4 and 16 by means of stainless steel support shafts l8 and 20, respectively. Rolls 14 and 16 are rotatable in opposite directions about spaced parallel axes by means of meshing gears 22 and 24 carried on the shafts l8 and 20 respectively. Gear 22 is directly driven by an output shaft 26 of a selectively energizable drive motor 28. A power supply 30 has a high potential dc output line 32 electrically connected to the stainless steel shaft 18 by way of brushes 34. A ground line 36 is electrically connected to stainless steel shaft 20 by way of brushes 38. Accordingly, an electrical path between lines 32 and 36 extends through the stainless steel shafts l8 and 20 and the rolls l4 and 16 and any substance such as sheets of paper passed between the rolls l4 and 16.

Referring specifically to FIG. 2, the composition of the roll 14 and 16 is indicated in greater detail. Roll 14 is shown to comprise a thick radially outer portion 40 of sintered clay-base ceramic material doped with iron oxide. The inner diameter surface 42 of outer portion 40 is metalized such as by plating with nickel to form a good electrical contact with a conductive filler material 44. The conductive filler material 44 is mechanically and electrically connected to the stainless steel shaft 18. Roll 14 is in peripheral contact with roll 16 which is a unitary or solid hollow cylinder of conductive material disposed on the stainless steel shaft 20 and being mechanically and electrically connected thereto.

Roll 16 is preferably fabricated in accordance with the following steps.

As a first step, the materials are thoroughly blended such as by milling in the following percentages by weight: 5.6 percent talc, 14.5 percent kaolin, 12.1 percent ball clay, 28.1 percent feldspar, 20.1 percent silica, and 19.6 percent iron oxide (Fe*0").

As a second step, the following materials and quantities by weight are added to the mill: 1.4 percent denatured ethyl alcohol, 97 percent deionized water, an anti-foam emulsion, and, in some instances a small amount of wax.

This mixture is milled and mixed for approximately 12 hours to produce a slurry or slip having a viscosity measured by the flow of 210 milliliters in 38 seconds and having a slip weight of 732 grams for each 500 milliliters and a slip screen of minus mesh.

The slip is spray dried to form a fine powder and then isostatically pressed or mechanically compacted at pressures of between 10,000 and 20,000 pounds per square inch to form the hollow cylindrical roll 14. A pressing schedule of 5 minutes increasing pressure, 1 minute dwell and 30 seconds decreasing pressure may be employed.

The next step involves the firing or sintering of the formed roll 14. This is accomplished by means of a conventional kiln suitably provided with thermostats for temperature measurement and temperature control. The kiln is heated at a rate of approximately 40 centigrade per hour until a maximum temperature of 1,100" C. is reached. This temperature is maintained for approximately 15 hours and then reduced.

After the firing, both inner and outer surfaces of the roll 14 are generally smooth and glassy. It is necessary to etch the surfaces in order to provide a suitably receptive inner diameter surface for metalizing and to eliminate non-uniformity of electrical resistivity due to glassy spots on the outer diameter surface. Such etching is accomplished by cleaning the rolls ultrasonically for approximately 5 minutes in an alkaline detergent and then etching the roll 14 in a boiling 20 percent solution of NaOH for 15 minutes.

The next step is to metallize the inner diameter surface 42 of the roll 14. This is preferably accomplished by means of an electroless nickel plating process which involves the application of a sensitizer, an activator and an electroless nickel plate bath. Nickel plating of the end and outer diameter surfaces which may result is eliminated by plugging the ends of the roll 14 and immersing it in a 50 percent nitric acid solution.

The next step is to assemble the metalized roll 14 to the stainless steel shaft 18. This is preferably accomplished by means of the conductive filler 44 similar to a conductive epoxy which establishes a good mechanical and electrical connection between the stainless steel shaft 18 and the roll 14. The filler material 44 is a solder, preferably an alloy of 58 percent bismuth and 42 percent tin having a positive thermal expansion coefficient. The stainless steel shaft 18 may be sandblasted to provide the surface which will result in a good mechanical bond to the conductive filler 44.

Referring again to FIG. 1, the operation of the copying assembly will be described in general terms since the subject electrostatic copying process is well-known to those of ordinary skill in the art. A sheet of paper containing printed matter or the like which is to be copied is inserted between the rolls l4 and 16 along with an adjacent sheet of zinc-oxide coated paper upon which the copy is to be made. The pressure of the paper between rolls l4 and 16 produces a small capacitive gap. The motor 28 is energized so as to drive the two adjacent pieces of paper between the roles l4 and 16. a charge of approximately 4,000 volts is electrostatically induced across the roll gap, i.e., between the opposite plane surfaces of the paper by passage between the positively charged roll 14 and the grounded roll 16. The zinc-oxide coated paper is then exposed to the original printed matter to be copied by means of a lens system not shown. The zinc-oxide coated paper is also previously treated with photoconducting dyes which sensitize the zinc-oxide to visible light. Accordingly, the charged copying paper is exposed to the image and light from a light source 46, the non-image areas of the paper rapidly dissipate the charge induced across the paper. Following this step, the copy paper is passed to a developer stage 48. in this developer stage 48, the paper may be exposed to a brushed or sprayed-on mixture of pigmented resin and iron particles which adheres to the negatively charged areas of the paper. The iron and resin mixture is heat fused into the paper to complete the development process.

it is to be understood that the specific embodiment described herein is given by way of example and is not to be construed in a limiting sense.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In an electrostatic copying assembly: first and second rolls adjacently mounted for rotation about parallel axes; said first roll having a body of fired ceramic material comprising a major constituent consisting of a mixture of clay and feldspar and a minor constituent uniformly dispersed throughout the major constituent and consisting of iron oxide, the major constituent constituting at least 51 percent of the dry weight of the ceramic material; said second roll being of a conductive material; and means for establishing a relatively high voltage gradient radially between the l'l ig gg r aiii defined in claim 1 wherein the major constituent comprises at least approximately 14.5 percent kaolin. 12.1 percent ball clay, and 28.1 percent feldspar.

3. The apparatus as defined in claim 1 wherein said first roll is of a hollow, cylindrical configuration defining an interior surface, and a conductive metal unifomtly disposed over the interior cylindrical surface.

4. For use in an electrostatic copying assembly: a cylindrical roll of uniformly resistive fired ceramic material comprising a major constituent consisting of a mixture of clay and feldspar and a minor constituent uniformly dispersed throughout the major constituent and consisting of iron oxide, the major constituent constituting at least 50 percent of the dry weight of the ceramic material, the roll having a substantially hollow cylindrical configuration to define an interior cylindrical surface and a conductive metal disposed over said inner cylindrical surface.

5. The roll defined in claim 4 wherein the major constituent comprises at least about 14.5 percent kaolin, l2.l percent ball clay, and 28.l percent feldspar.

6. For use in an electrostatic copying assembly: a cylindrical roll of uniformly resistive fired ceramic material comprising a major constituent consisting of silicate clay material and a minor constituent uniformly dispersed throughout the major constituent and consisting of finely divided conductive metal oxide, the major constituent constituting at least 5 1 percent of the dry weight of the ceramic material, the roll having a substantially hollow cylindrical configuration to define an interior cylindrical surface and a conductive metal disposed over said inner cylindrical surface. 

2. The apparatus defined in claim 1 wherein the major constituent comprises at least approximately 14.5 percent kaolin, 12.1 percent ball clay, and 28.1 percent feldspar.
 3. The apparatus as defined in claim 1 wherein said first roll is of a hollow, cylindrical configuration defining an interior surface, and a conductive metal uniformly disposed over the interior cylindrical surface.
 4. For use in an electrostatic copying assembly: a cylindrical roll of uniformly resistive fired ceramic material comprising a major constituent consisting of a mixture of clay and feldspar and a minor constituent uniformly dispersed throughout the major constituent and consisting of iroN oxide, the major constituent constituting at least 50 percent of the dry weight of the ceramic material, the roll having a substantially hollow cylindrical configuration to define an interior cylindrical surface and a conductive metal disposed over said inner cylindrical surface.
 5. The roll defined in claim 4 wherein the major constituent comprises at least about 14.5 percent kaolin, 12.1 percent ball clay, and 28.1 percent feldspar.
 6. For use in an electrostatic copying assembly: a cylindrical roll of uniformly resistive fired ceramic material comprising a major constituent consisting of silicate clay material and a minor constituent uniformly dispersed throughout the major constituent and consisting of finely divided conductive metal oxide, the major constituent constituting at least 51 percent of the dry weight of the ceramic material, the roll having a substantially hollow cylindrical configuration to define an interior cylindrical surface and a conductive metal disposed over said inner cylindrical surface. 